1. Field of the Invention
This invention relates to a barrier layer and to a method of depositing a barrier layer on a substrate having a recess.
2. Description of the Related Art
Ta and Ta(N) films deposited by physical vapour deposition (PVD), are widely used as diffusion barriers in Cu metallisation systems, in, for example semiconductor devices. A great deal of research has been done on the formation of various Ta(N) phases as the amount of N2 incorporated into the Ta structure is increased. The material systems which are formed are complex, varying from films that are best described as N2 in a solid solution with Ta to polycrystalline phases of Ta(N) such as Ta4N, Ta2N and TaN. The investigations reported in the literature into the barrier properties of such layers, in their different phases, are almost all based on a blanket deposition on the field of the wafer, and little or no investigation has taken place into the properties of the barrier in the actual integrated structure when recesses, such as vias, are formed and have to be coated.
In reality, the performance in the integrated structure is an important consideration when Cu metallization is used, since Cu, unlike Al has a high diffusivity into SiO2-based dielectrics. Consequently, the characteristics and integrity of the barrier materials deposited on the sidewalls of a via or trench is of significant importance in preventing the undesirable diffusion of Cu into the dielectric.
The current prior art understanding is that the best barrier layers are formed when Ta is sputter deposited in high flows of nitrogen in a mix with inert gas such as argon, but this understanding seems to be based on a comparison of the barrier layer properties on the basis of unit thickness of barrier layer without consideration for the resultant thicknesses of the different Ta(N) phases deposited on the side walls of sub-micron recesses in insulating layers.